The present invention relates generally to bladed disk (blisk) turbine components and, more specifically, to a method and apparatus for making integral turbine components comprising a ring of single crystal airfoils with small angle grain boundaries located in the endwalls between adjacent airfoils.
Superalloy turbine disks are often used for commercial gas turbine engines. Commonly, turbine disks are machined from forged fine-grained equiaxed superalloy castings or from consolidated and forged superalloy powder. Disk alloy compositions are selected based on their combination of their resistance to creep and fatigue at temperatures below about 1400 degrees F. (760 degrees C.). Single crystal superalloys provide superior high temperature creep strength in the temperature range of 1400 F. (760 degrees C.) to 2100 F. (1149 degrees C.), and are consequently preferred for turbine airfoil applications. However, attempts to use single crystal airfoils in integral turbine bladed disks and nozzles have been hampered by inadequate grain boundary strength between adjacent single crystal airfoils, which necessitated unacceptably high manufacturing cost and high costs for casting and machining individual airfoils and bonding the individual airfoils into a bladed ring or nozzle. Prior art turbine blisks comprise individually cast blades that have machined fir tree or dovetail attachments which permit insertion into mating machined slots in the circumference of the rim of the disk. High temperatures and attachment stresses require machining the individual blades and slots to tight tolerances. This involves excessive labor and time. Dual alloy blisks composed of a cast equiaxed superalloy blade ring bonded to a high-strength disk alloy are also prior art. However, the cast equiaxed airfoils limit the temperature capability and performance of the turbine. Single crystal superalloys can maintain metal capabilities at temperatures of up to 100 degrees Fahrenheit (38 degrees C.) or more above the maximum temperature ranges of equiaxed materials.
None of the prior art is specifically intended for high performance applications under extreme conditions, and some suffer from one or more of the following disadvantages;    a) excessive mass and size.    b) inability to sustain high temperature conditions.    c) increased labor costs to address mechanical tolerances.    d) low creep strength at high temperatures.    e) short rupture life.    f) inadequate grain boundary strength between adjacent airfoils.    g) low casting yields.
As can be seen, there is a need for an improved apparatus and method for turbine components comprising single crystal airfoils with reduced crystallographic misorientation between adjacent airfoils, is lower in mass and size than prior art components, withstands higher temperatures and extreme conditions, has high creep strength and rupture life, high grain boundary strength between adjacent airfoils, and enables high casting yields and lower manufacturing cost.